This invention relates to electronics, in general, and to semiconductor components and methods of manufacture, in particular.
In applications such as Liquid Crystal Display (LCD) display drivers, the source, body, gate, and drain terminals of a Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) must be able to sustain high voltages of fifteen volts or greater relative to each other and relative to the semiconductor substrate in which the MOSFET is formed. One skilled in the art will understand that FIG. 1. illustrates a cross-sectional view of a MOSFET 100 that is suitable for high voltage applications involving voltages greater than approximately fifteen volts. MOSFET 100 is manufactured using an older semiconductor technology that uses a semiconductor substrate 110 that does not include an epitaxial layer. Semiconductor substrate 110 has an P-type conductivity with a low doping concentration referred to as Pxe2x88x92.
MOSFET 100 is bi-directional and symmetric and is an N-type MOSFET or NMOS transistor. One skilled in the art will understand that appropriate changes can be made to the description of MOSFET 100 if MOSFET 100 were a P-type MOSFET or PMOS transistor. MOSFET 100 includes a gate electrode 160, a gate oxide 170, and field oxide regions 180 and 190. MOSFET 100 also includes four deep diffused wells 120, 130, 140, and 150 to isolate MOSFET 100 from other transistors in semiconductor substrate 110. Wells 120, 130, and 150 have an N-type conductivity, and well 140 has a P-type conductivity. The deep-diffused wells, however, are not compatible with modern deep sub-micron device technologies because of the imprecision of the diffusion process.
One skilled in the art will understand that FIG. 2 illustrates a cross-sectional view of a MOSFET 200 that is also suitable for high voltage applications. MOSFET 200 is manufactured using a more modern deep-submicron semiconductor technology that uses a semiconductor substrate 210 that includes a support substrate 211 and an epitaxial layer 212. Support substrate 211 has a P-type conductivity and has a very high doping concentration referred to as P+ to minimize a latch-up problem during operation of MOSFET 200. Epitaxial layer 212 has a Pxe2x88x92 conductivity.
MOSFET 200 is bi-directional and symmetric and is an N-type MOSFET or NMOS transistor. One skilled in the art will understand that appropriate changes can be made to the description of MOSFET 200 if MOSFET 200 were a P-type MOSFET or PMOS transistor. MOSFET 200 includes a gate electrode 260 and field oxide regions 280 and 290. MOSFET 200 is formed in epitaxial layer 212, but epitaxial layer 212 is too thin to contain the multiple deep diffused wells described earlier for the older semiconductor technology in FIG. 1. Instead, MOSFET 200 in FIG. 2 includes more shallow N-type conductivity wells 220 and 230.
To permit MOSFET 200 to operate under high voltage conditions, MOSFET 200 typically includes an extra P-type region 240. MOSFET 200 also typically includes a gate oxide 270 that is thicker than that required for gate oxide 170 of MOSFET 100 in FIG. 1 to provide the high voltage compatibility for MOSFET 200 in FIG. 2. Gate oxide 270 may require a thickness of approximately forty nanometers in order to support a twelve volt breakdown voltage.
This thicker gate oxide, however, is approximately four times the thickness of gate oxides for typical MOSFETs. Therefore, a new process module must be inserted into the manufacturing process to be able to integrate MOSFET 200 into an integrated circuit with other MOSFETs. This new process module increases the cost, complexity, and cycle time for the manufacturing process of the semiconductor component containing MOSFET 200.
The thicker gate oxide also requires a larger gate-to-source operating voltage, approximately twelve volts, to fully drive MOSFET 200. Therefore, a higher voltage power supply must also be used for the integrated circuit containing MOSFET 200. This higher voltage power supply increases the application costs and also decreases the application convenience for MOSFET 200.
Furthermore, the channel region underneath the thicker gate oxide in MOSFET 200 is not isolated from, but is electrically shorted to, other portions of semiconductor substrate 210 such as support substrate 211. Therefore, the electrical performance of MOSFET 200 will be degraded by the other devices in semiconductor substrate 210. Additionally, at least the gate terminal of MOSFET 200 may not be capable of sustaining high voltages of fifteen volts or greater relative to support substrate 211.
Accordingly, a need exists for a semiconductor component suitable for use in high voltage applications, particularly where a semiconductor device in the semiconductor component has electrodes that are capable of sustaining high voltages relative to each other. A need also exists for a method of manufacturing the semiconductor component.